1. Field of the Invention
Embodiments of the invention relate to power conversion and, more particularly, to a resonant power converter circuit.
2. Description of the Related Art
Generally, as shown in FIG. 1, a DC-AC resonant power converter 100 comprises a bridge circuit 102 and resonant circuit 104 on the “DC side” 120 and a cyclo-converter circuit 108 on the “AC side” 122. As is well known in the art, the power converter circuit 100 can be used for DC to AC conversion or AC to DC conversion. Thus, the left side may be coupled to either a DC source or DC load and the right side can be coupled to an AC load or AC source.
A transformer 106 couples the two sides to one another—a primary winding 106-P is connected to the DC side and a secondary winding 106-S is connected to the AC side. A first terminal of the secondary transformer winding 106-S couples to one terminal of three bidirectional switches 110-1, 110-2, and 110-3. A second terminal of each of the three switches 110-1, 110-2, and 110-3 is connected to one of the three phases (live conductor lines L1, L2, and L3) of an AC source or load. The second terminal of the transformer secondary winding 106-S is connected to a neutral point (neutral line N) that can be connected to the AC source/load or not.
Bypass capacitors 112-1, 112-2, and 112-3 are connected from neutral line N to the respective lines L1, L2, and L3. Capacitors may be connected across each switch in the case of an LCC type resonant converter. One issue with this resonant converter circuit topology is that bidirectional switches are not commercially readily available and must be implemented with back-to-back unidirectional switches such as metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), bipolar junction transistors (BJTs), and the like. These switches have to be driven from the midpoint which swings at very high speed. In turn, such a midpoint drive creates undue drive circuit complexity as the required isolation needs to withstand very high dV/dt common mode voltages. Consequently, the drive circuit requires high isolation voltage supplies, fiber optic connections, and the like. Such complexity increases the cost of the resonant power converter.
Therefore, there is a need in the art for a resonant power converter that mitigates the foregoing problems.